In conventional positioning systems, whether to perform the process with respect to averaged results of a plurality of positioning calculations or to perform the process with respect to a result of a single positioning calculation is determined according to the setting as described in, for example, Japanese Patent Application laid open No. 2001-333445 and Japanese Patent Application laid open No. 2001-339755.
Besides, in the case where accuracy is required of positioning, the averaging process is carried out as described in, for example, Japanese Patent Application laid open No. 2002-281540 and Japanese Patent Application laid open No. 2002-296339.
FIG. 1 is a block diagram showing the configuration of a conventional mobile phone unit provided with a GPS (Global Positioning System). With reference to FIG. 1, a description will be made of the configuration of a conventional GPS mobile phone unit.
As can be seen in FIG. 1, a GPS mobile phone unit 31 comprises a GPS antenna 11 for receiving GPS signals, a GPS radio section 12 for demodulating the GPS signals, a GPS decryption section 13 for decrypting the GPS signals, a two-way transmission antenna 14 for transmitting/receiving radio signals of a mobile phone system, a frequency supply block 17, a mobile phone radio section 32 for modulating/demodulating the radio signals, a system processing section 33 for performing the processing of mobile phone signals and the processing of GPS signals, a voice input/output section 18, a voice processing section 19, a display 20, a display processing section 21, a CPU 34 for executing overall processing, and a real time clock (RTC) 35 for executing the time of day control of the GPS mobile phone unit 3.
FIG. 2 is a flowchart showing the positioning operation carried out by the GPS mobile phone unit 31 shown in FIG. 1.
When the positioning operation starts (step S81), the system processing section 33 determines whether to perform the process with respect to averaged results of a plurality of positioning calculations or to perform the process with respect to a result of a single positioning calculation (step S82). The system processing section 33 makes a decision on the process to be carried out based on predetermined settings.
When the process with respect to averaged results of a plurality of positioning calculations is performed, after the initialization process (step S83) and positioning calculation (step S84), the positioning process including the averaging process is implemented (steps S85 to S88).
When the process is performed using a result of a single calculation, after positioning calculation (step S89), a positioning result is output (step S90).
In the aforementioned conventional system, a decision as to whether to perform the process with respect to averaged results of a plurality of positioning calculations or to perform the process with respect to a result of a single positioning calculation is made according to predetermined settings regardless of the state of the mobile phone unit. Consequently, an optimum calculation result cannot be obtained.
In addition, for example, if the averaging process is simply carried out in the case of positioning which requires accuracy, an error occurs due to the averaging when the mobile phone unit is in transit. However, if the averaging process is performed on the ground that the mobile phone unit is in transit, it takes extra time to carry out positioning calculations, and, therefore, previous location information which has already been obtained is used as the output of a positioning result.
On the other hand, when employing a result of a single positioning calculation, a notification of positioning failure is given in situations that the rate of successful positioning is low, and a utility sphere or area is restricted.